Media compositions for eluting compounds from matrices and methods for making and using them

ABSTRACT

Embodiments of the invention provide to apparatuses and media used in drug elution studies and methods for making and using them. One embodiment of the invention is a drug elution method that can be used for in-vitro studies of a matrix impregnated with a compound such as a drug blended polymer matrix. Such methods and materials can be used for example to assess and control the manufacturing process variability of drug eluting implantable devices such as cardiac leads.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.11/881,074, and U.S. patent application Ser. No. 12/005,952, thecontents of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates to media compositions useful inelution studies (e.g. the elution of a drug from a polymeric matrix) andmethods for making and using them.

2. Description of Related Art

The implantation of a medical device into a patient's body can cause thebody to exhibit adverse physiological reactions ranging from infectionsto the formation of emboli or clots in blood vessels. One approach toaddress such reactions and improve the biocompatibility of such medicaldevices is to incorporate bioactive or pharmacological agents such assteroids, and/or antibiotics and/or anticoagulants onto a surface ofthese devices. Once implanted, these agents can then elute into the invivo environment at the site of implantation and modify thephysiological response.

Exemplary medical procedures that involve the implantation of medicaldevices include those designed to modulate cardiac physiology. Forexample, a variety of systems that use one or more pacing leads withelectrodes such as cardiac rhythm management (CRM) systems and varioustechniques for implanting these lead systems in contact body tissue suchas the heart, have been developed. In this context, the safety, efficacyand longevity of an electrical pulse generator of a CRM depends, inpart, on the performance of the associated cardiac lead(s) used inconjunction with the pulse generator. For example, various properties ofthe lead and electrodes will result in a characteristic impedance andstimulation threshold. Stimulation threshold is the energy required in astimulation pulse to depolarize, or “capture,” the heart tissue. Arelatively high impedance and low threshold is desired to minimize thecurrent drawn from a pulse generator battery in delivering a stimulationpulse. Another example may be when implanting a medical device, it canresult in infections in the area of infections. Such infections can bereduced by coating or otherwise combining an antibiotic with theimplanted device.

One factor that can affect the stimulation threshold, particularlyduring the first several weeks after implantation of a lead, is thenatural immunological response of the body to the lead as a foreignobject. The presence of the lead activates macrophages, which attachthemselves to the surface of the lead and any electrodes and formmulti-nucleated giant cells. These cells, in turn, secrete varioussubstances, such as hydrogen peroxide as well as various enzymes, in aneffort to dissolve the foreign object. Such substances, while intendingto dissolve the foreign object, also inflict damage to the surroundingtissue. When the surrounding tissue is the myocardium, these substancecause necrosis. These areas of necrosis, in turn, impair the electricalcharacteristics of the electrode-tissue interface. Consequently pacingthresholds rise. Even after the microscopic areas of tissue die theinflammatory response continues and approximately seven days afterimplant the multi-nucleated giant cells cause fibroblasts to beginlaying down collagen to replace the necrotic myocardium. Eventually, onthe order of three weeks after implant, the lead and its electrodes canbe encapsulated by a thick layer of fibrotic tissue. Typically, theinflammatory response ends at this time. The fibrotic encapsulation ofthe lead and its electrodes, however, remains. Since the fibrotic tissueis not excitable tissue, an elevated stimulation threshold can persistdue to the degraded electrical properties of the electrode-tissueinterface.

One means of modulating this inflammatory response in implanted cardiacrhythm management systems has been to provide a drug near the electroniclead to mitigate the inflammatory tissue reaction described above. Inparticular, it has been found devices designed to elute ananti-inflammatory agent, such as a glucocorticoid steroid, minimizetissue irritation, help reduce or eliminate threshold peaking andfurther assist in maintaining low acute and chronic pacing thresholds. Aconsiderable breakthrough in the development of low threshold electrodetechnology occurred with the invention of the steroid eluting pacingelectrode of Stokes U.S. Pat. No. 4,506,680 and related Medtronic U.S.Pat. Nos. 4,577,642, and 4,606,118. Steroid, it is believed, inhibitsthe inflammatory response by inhibiting the activation of themacrophages. Because they do not form multi-nucleated giant cells, thesubsequent release of substances to dissolve the object and which alsodestroy the surrounding tissue is prevented. Thus, the necrosis of anytissue by the inflammatory response is minimized as well as theformation of the fibrotic capsule. Minimizing such adverse reactions ishighly desirable because it also minimizes the concomitant deteriorationof the electrical characteristics of the electrode-tissue interface. Theincorporation of a compound such as a steroid that elutes at the site ofimplantation permits pacing leads to have a source impedancesubstantially lower as compared to leads featuring similarly sized solidelectrodes. Consequently, electronic leads which can elute compoundssuch as steroids also present significantly lower peak and chronicpacing thresholds than similarly sized electrodes and have thereforebeen adapted for patient treatment in a variety of contexts.

Implantable compositions which elute a steroid can include a drugblended with a polymeric material such as dexamethasone impregnatedwithin a silicone polymer, a blended composition that is designed toslowly elute the steroid out of the polymer and into the surroundingtissue. Incorporating a drug such as a steroid into a device so that itwilt elute from a device upon implantation, however, increases thecomplexity of electronic device production as compared to non-steroideluting devices. One potential area of difficulty in this context is thepossibility of variable manufacturing processes and the potentialassociated effects on elution kinetics. In this context, methods andmaterials that allow artisans to readily examine the drug elutionproperties of electronic devices and other drug eluting medical devicesare highly desirable. Such methods and materials can be used for exampleto assess manufacturing process variability of drug eluting implants andthe associated quality control of such processes. Moreover, while realtime in vivo elution studies may be necessary to gain a comprehensivemechanistic understanding of the modulation of the physiologicalreactions observed with implantation, such real time elution tests canbe on the order of weeks or months. Consequently, accelerated in-vitrotests that correlate with such tests are important for manufacturing andquality control processes. For this reason, methods and materials suchas media compositions that can be used to assess and control themanufacturing process variability of drug eluting implantable devicesare highly desirable.

SUMMARY OF THE INVENTION

Embodiments of the invention provide media compositions useful for drugelution studies and methods for making and using them. The media andassociated methods disclosed herein are designed for the elution ofagents impregnated within a polymer matrix. Such methods and materialscan be used, for example, to assess and control the manufacturingprocess variability of drug eluting implantable devices such as cardiacleads.

One embodiment of the invention is a drug elution method that can beused for in-vitro studies of a matrix impregnated with a compound suchas a drug blended polymer matrix. Illustrative embodiments of theinvention include methods that use a unique dissolution media to observethe elution of dexamethasone sodium phosphate from a blended polymer, amatrix that can be used for example with drug loaded pacemaker leads.This dissolution media uses a combination of constituents designed toelute compounds from within a matrix effectively and efficiently over arelatively short period of time. This dissolution media and methods forusing it consequently provide an in-vitro platform for productdevelopment and quality control, particularly in the production of drugcoated/impregnated medical devices.

An illustrative embodiment of the invention is a method for observingthe elution of a compound from a matrix, the method comprising exposingthe matrix comprising the compound to a solution comprising: 20-40% of alower alkanol (e.g. isopropanol); and 0.2-6.0% of a matrix swellingagent; and then assaying the solution for the presence of the compoundso as to observe the elution of the compound from the matrix into thesolution (e.g. via a chromatographic separation technique such as HPLC).In illustrative embodiments of the invention, the matrix swelling agentcomprises 0.2-1.0% diisopropyl amine; and/or dipropylamine; and/ortetramethylethylenediamine; and/or tributylamine; and/or 0.5-6% benzylalcohol. Typically, the solution further comprises a buffer such asphosphate buffer having a pH range of pH 6 to pH 8. In one illustrativeembodiment of the invention, the solution comprises 0.05M potassiumphosphate buffer at pH 8; 30% isopropyl alcohol; and <1% benzyl alcohol;or <1% diisopropylamine.

The methodological embodiments of the invention can be used to study theelution of a wide variety of compounds from a wide variety of matrices.For example, the method can be used to study a plastic or otherpolymeric matrix having the compound impregnated, coated or embeddedtherein. In an illustrative embodiment, the matrix can comprise apolymer such as a silicone or polyurethane polymer and the compound cancomprise a steroid, an anti-coagulant an antibiotic, or ananti-inflammatory agent. In an illustrative embodiment provided in theexamples below, the matrix is a biomedical grade silicone polymerimpregnated with dexamethasone sodium phosphate. Typically, the matrixand the compound are adapted for implantation in vivo, for example aspart of an electronic lead of a pacemaker.

In typical embodiments of the invention, the methods are adapted tofacilitate processes such as the product development and quality controlof implantable drug coated medical devices. In such embodiments, themethod can be practiced on a plurality of matrices produced according toa uniform manufacturing process, typically one designed to produce aplurality of matrices that elute the compound at the same rate.Optionally, the method can include the step of comparing the elutionrates of two or more matrices to impregnate with a compound such asdexamethasone sodium phosphate so as to determine if the two or morematrices have the same or different elution rates.

A related embodiment of the invention is a composition of mattercomprising an aqueous solution of 20-40% of a lower alkanol; and one ormore matrix swelling agents comprising: 0.2-1.0% diisopropyl amine;0.2-1.0% dipropylamine; 0.2-1.0% tetramethylethylenediamine; 0.2-1.0%tributylamine; and/or 0.5-6% benzyl alcohol. In certain embodiments ofthis composition, the solution comprises 0.03 to 0.05M potassiumphosphate buffer having a pH range of pH 6 to pH 8; 30% isopropylalcohol; <1% benzyl alcohol; and/or <1% diisopropylamine. In someembodiments of the invention, the composition of matter furthercomprises a matrix impregnated with an elutable agent comprising asteroid, an anti-coagulant an antibiotic, or an anti-inflammatory agent.Optionally for example, the matrix is a polymer matrix impregnated withdexamethasone sodium phosphate. In one illustrative embodiment of theinvention, the composition further comprises a polymer matrix adaptedfor use as part of a cardiac lead.

A related embodiment of the invention is the use of the disclosed mediacompositions in an apparatus that, for example, can facilitate thepractice of the above-noted methods by inhibiting the evaporation ofdissolution media from the vessels in which elution is observed. Inparticular, the apparatus includes a cap designed to cover the vesseland inhibit dissolution media loss through evaporation (see, e.g. FIG.7). Typically, the cap has a sample port which can optionally functionas a temperature measuring port. In illustrative embodiments of theinvention, a sampling cannula is introduced using this port such thatthe point of sampling inside the vessel can be easily adjusted. In otherembodiments of the invention, the apparatus has a separate port whichacts as a temperature member port. This evaporation loss cover apparatusoffers easy and accurate sampling, measuring temperature and virtuallyno loss due to evaporation. In illustrative embodiments of theinvention, the apparatus dramatically reduces evaporation to less than1% over a one-week test period.

Embodiments of the invention also provide articles of manufactureincluding media system kits. In one such embodiment of the invention, akit including the reagents disclosed herein and useful for elutionstudies, is provided. The kit typically comprises a container, a labeland elution reagents as described above.

Other objects, features and advantages of the present invention will beapparent to those skilled in the art from the following detaileddescription. It is to be understood, however, that the detaileddescription and specific examples, while indicating some embodiments ofthe present invention are given by way of illustration and notlimitation. Many changes and modifications within the scope of thepresent invention may be made without departing from the spirit thereof,and the invention includes all such modifications.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an exemplary profile of a compound eluting from a matrix,specifically the elution of dexamethasone sodium phosphate from a drugeluting matrix used with implantable medical devices. In this study, theconditions comprised: 30% iPA+0.5% benzyl Alcohol in Phosphate Buffer,pH 8.0

FIG. 2 shows the impact of process changes on the elution profiles ofdexamethasone sodium phosphate from differing lots of drug elutingdevices. In this elution discrimination study, the conditions comprised:30% iPA+0.5% benzyl Alcohol in Phosphate Buffer, pH 8.0.

FIG. 3 shows an exemplary elution profile of dexamethasone sodiumphosphate from a drug eluting device matrix. In this elutiondiscrimination study, the conditions comprised: 30% iPA+0.5% DIPA+0.5%Benzyl Alcohol in Phosphate Buffer, pH 8.0 at 45° C.

FIG. 4 shows the impact of process changes on elution profiles ofdexamethasone sodium phosphate from differing lots of drug elutingdevices. In this elution discrimination study, the conditions comprised:30% iPA+0.5% DIPA+0.5% Benzyl Alcohol in Phosphate Buffer, pH 8.0 at 45°C.

FIG. 5 shows an exemplary Elution Profile of Dexamethasone SodiumPhosphate from a drug eluting device. In this study, the conditionscomprised 30% iPA+0.3% DIPA in Phosphate Buffer, pH 8.0 at 45° C.

FIG. 6 shows the impact of process changes on elution profile ofdexamethasone sodium phosphate from different lots of drug elutingdevices. In these elution discrimination studies, the conditionscomprised 30% iPA+0.3% DIPA in Phosphate Buffer, pH 8.0 at 45° C.

FIG. 7 shows an apparatus that can be used in methods of the invention,one designed to inhibit fluid loss due to evaporation from a fluiddissolution vessel. This specific embodiment of the apparatus (10)comprises a cap (20) for engaging a vessel (30). The central diagramshows a group of four caps operative engaged with vessels and variousinteractive elements of the apparatus. The diagram at the upper rightshows the cap not engaged with a vessel and/or various interactiveelements of the apparatus. In the embodiment of the invention shown inthis figure, the cap has a first external side (40) and a secondinternal side (50) that is exposed to a fluid contained in the vessel.The second side (50) comprises a conical member (60) that is designed todirect a condensate that has condensed from the fluid in the vessel ontothe second side of the cap back into the fluid. The cap includes aflange (70) disposed between the first external side and the secondinternal side of the cap. This embodiment shows a central port (80)disposed in the cap adapted to receive a rotatable rod (90), where thematerial of the central port (typically Teflon) and the material of therotatable rod are in close contact so as to create a seal that inhibitsescape of a material contained within the vessel into the externalenvironment. The rotatable rod in this embodiment includes a fluidagitation member (170) at the distal end of the rod that agitates fluidwithin the vessel. In this embodiment, the central port (80) is disposedin a central washer (120) that is further disposed within a centralwasher port (130) on the cap. This embodiment shows a sample port (100)disposed in the cap to allow a user to obtain a sample of the solutionfrom the vessel (or to introduce a composition into the vessel) via acannula (not shown). In this embodiment, the sample port (100) isdisposed in a sample port washer (110) that is further disposed in asample washer port (160). The sample port washer (110) further includesa cannula securing port (140) that receives a tightening screw member(not shown) that can be used to secure a cannula inserted into thesample port (100) at a desired position. This embodiment further shows atemperature member port (150) adapted to allow a user to introduce atemperature member that contacts and monitors the temperature of thesolution within the vessel. The temperature member port (150) is adaptedto receive a temperature port cap (210) that can cover the temperatureport to inhibit escape of a material within the vessel into the externalenvironment. All of the interacting components in this embodiment of thecap (20) are constructed to closely fit together so as to create sealsthat inhibits escape of a material within the vessel into the externalenvironment. In addition, a sealing member (not shown) that contacts thevessel (30) that contains the fluid can also be disposed on the cap (20)so as to create a seal with the vessel that inhibits escape of amaterial within the vessel into the external environment when the cap isoperatively engaged with the vessel. The embodiment of the apparatus inthis figure further shows a clamp (180) that secures the cap to thevessel via a clamp screw member (190) as well as a rack (200)constructed to hold a plurality of vessels.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Unless otherwise defined, all terms of art, notations and otherscientific terms or terminology used herein are intended to have themeanings commonly understood by those of skill in the art to which thisinvention pertains. In some cases, terms with commonly understoodmeanings are defined herein for clarity and/or for ready reference, andthe inclusion of such definitions herein should not necessarily beconstrued to represent a substantial difference over what is generallyunderstood in the art. Many of the techniques and procedures describedor referenced herein are well understood and commonly employed usingconventional methodology by those skilled in the art. As appropriate,procedures involving the use of commercially available kits and reagentsare generally carried out in accordance with manufacturer definedprotocols and/or parameters unless otherwise noted.

A. Methods and Media for Observing Drug Elution from a Matrix

The invention disclosed herein has a number of embodiments. Oneembodiment of the invention is a drug elution method that can be usedfor in-vitro studies of a matrix impregnated with a compound such as adrug blended polymer matrix. Specific embodiments of the inventioninclude methods that use a unique media system to observe the elution ofdexamethasone sodium phosphate from a drug blended polymer matrix, amatrix that is used for example with drug loaded pace maker leads. Thisdissolution media uses a combination of constituents designed to elutecompounds from within a matrix effectively and efficiently over arelatively short period of time. This dissolution media and methods forusing it consequently provide an in-vitro platform for productdevelopment and quality control, particularly in the production of drugcoated medical devices.

The data disclosed in FIGS. 1-6 provides illustrative embodiments of themethods of invention that examine the elution of dexamethasone sodiumphosphate from a polymeric silicone matrix. These examples provide anillustration of the power of the methodological embodiments of theinvention, in particular in view of the fact that the elution ofdexamethasone sodium phosphate from silicone polymer/drug coated pacemaker leads is known to be minimal in conventional solvents. Forexample, certain elution media and methods may not be ideal for alldrugs (e.g. dexamethasone sodium phosphate). For example, dexamethasonesodium phosphate is water soluble whereas typical methodologiesdescribed in the art are more suitable for water insoluble or sparinglysoluble drugs. Certain media constituents (e.g. sodium lauryl sulfate(SDS) and limonene), may not work well when elute dexamethasone sodiumphosphate from drug eluting devices (devices where drug is molded withpolymer). Consequently, the media compositions disclosed herein weredeveloped to overcome limitations with certain combinations of specificmedia compositions and specific agents as well to facilitatecomprehensive studies for in-vitro drug elution from drug elutingdevices. In this context, the new media compositions provide us enhancedelution properties for drugs such as dexamethasone sodium phosphate.

The media compositions disclosed herein can comprise a number ofdifferent compounds and combinations thereof. Some embodiments of theinvention include an elution media containing a solvent in the form ofone or more lower alkanol compounds. As used herein the term “alkanol”refers to alkanes (saturated hydrocarbons with straight or branchedchain structures, with general formula CnH2n+2) having a hydroxyl group(—OH) moiety. As used herein the term “lower alkanol” refers to alkanolshaving 1-8 carbon atoms such as methanol, ethanol, propanol, butanol,pentanol, hexanol, heptanol, octanol or mixtures thereof. The term“lower alkanol” includes both straight chain alkanols having 1-8 carbonatoms such as 1-propanol (also known in the art as n-propanol) and1-butanol (also known in the art as n-butanol) etc. as well as isomerssuch as isopropanol, isobutanol, sec-butanol, tert butanol etc. Incertain embodiments of the invention, the lower alkanol is an amylalcohol (an organic compound with the formula C5H12O) such as1-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol,2,2-dimethyl-1-propanol, 3-pentanol, 2-pentanol, 3-methyl-2-butanol or2-methyl-2-butanol. In some embodiments of the invention, the loweralkanol is ethanol or n-butanol. In one specific embodiment of theinvention, the elution media comprises the lower alkanol isopropylalcohol (also called 2-propanol, isopropanol and isopropyl alcohol).Isopropyl alcohol (IUPAC name: propan-2-ol, CAS number 67-63-0) is anorganic compound having the formula C3H8 O and a molecular weight of60.10 g/mol.

Embodiments of the media compositions typically comprise a matrixswelling agent. The term “matrix swelling agent” is used according toits art accepted meaning and refers to a solvent having properties thatallow a matrix to swell so as to increase the porosity of the matrix andachieve a desired increase in elution kinetics. A wide variety of matrixswelling agents are known in the art. Such swelling agents include forexample organic acids, organic alkylated amines such asmethyl/ethyl/butyl and propylamines and organic alcohols. Specificswelling agents know in the art include for example trifluoroacetic acid(TFA) and hydrogen fluoride (HF), dichloromethane (DCM), acetonitrile(ACN), benzyl alcohol, limonene and isopropanol (IP). A number of theillustrative matrix swelling agents described below are those selectedfor their ability increase the porosity of matrices commonly disposed onimplantable medical devices such as polymeric silicones andpolyurethanes. In typical methodological embodiments of the invention,this type of polymeric material is contacted with the matrix swellingagent under condition and for a sufficient period of time to promoteswelling of the matrix thereby causing diffusion/migration of thecompound from the matrix into the surrounding media.

Some embodiments of the invention include an elution media containing anagent selected for its ability to swell a polymeric matrix used withimplantable medical devices so as to facilitate agent elution from thepolymeric matrix. In certain embodiments of the invention, the elutionmedia comprises diisopropyl amine as such a swelling agent.Diisopropylamine (IUPAC name: N-isopropylpropan-2-amine, CAS number108-18-9) is a secondary amine with the chemical formula(CH3)2HC—NH—CH(CH3)2 and a molecular weight of 101.19 g/mol. DIPA is forexample used in media compositions designed for embodiments of theinvention directed to silicon matrices because it is observed to be oneof the compounds that swells silicone to the greatest extend. In certainembodiments of the invention, the elution media comprises dipropylamine(also called N,N-Dipropylamine; N-Propyl-1-propanamine;Di-n-propylamine, CAS number 142-84-7) as a swelling agent. In certainembodiments of the invention, the elution media comprisestetramethylethylenediamine (also calledN,N,N′,N′-Tetramethylethylenediamine, CAS number 110-18-9) as a swellingagent. In certain embodiments of the invention, the elution mediacomprises tributylamine (also called N,N-Dibutyl-1-butanamine, CASnumber 102-82-9) as a swelling agent.

In certain embodiments of the invention, the elution media comprisesadditional compounds such as benzyl alcohol. Benzyl alcohol (IUPAC name:Phenylmethanol, CAS number 100-51-6) is an organic compound having theformula C6H5CH2OH and a molecular weight of 108.14 g/mol. Benzyl alcoholis partially soluble in water (4 g/100 mL) and completely miscible inalcohols and ether. In certain embodiments of the invention an agentsuch as Benzyl Alcohol can exhibit multiple functionalities in anelution methodology and can for example act as a swelling agent as wellas a preservative for dexamethasone sodium phosphate.

The media compositions disclosed herein can comprise a number ofdifferent buffers and combinations thereof. In certain embodiments ofthe invention, the elution media comprises a potassium (or sodium)phosphate buffer. Such buffers are well known in the art and readilyprepared by artisans in this technology. Typically for example, onestarts with powder stocks of the commercially available compounds:K2HPO4 and KH2PO4. The powder stocks are used to prepare two solutions.Molarity depends on the molarity of the final solution: if one ispreparing a solution of 0.05 M phosphate buffer, each of the two K2HPO4and KH2PO4 solutions can be made with molarity of 0.05M. The desired pHcan then be obtained by mixing the two solutions in the appropriate way(the K2HPO4 solution pH is more than 8, while the KH2PO4 solution pH isabout 6.8). In one illustrative elution buffer used with embodiments ofthe invention is made according to the following recipe. A 0.05 MPotassium Phosphate Monobasic Solution is first prepared by weighing 6.8grams of Potassium Phosphate Monobasic into a 1000 ml volumetric flask,diluting it with process water to volume, and mixing. A 0.05 M PotassiumPhosphate Dibasic Solution is then prepared by weighing 8.7 grams ofPotassium Phosphate Dibasic into a 1000 ml volumetric flask, diluting itwith process water to volume, and mixing. 0.05M Phosphate Buffer, pH 8.0is then prepared by carefully titrating the Potassium PhosphateMonobasic with the Potassium Phosphate Dibasic solution until pH 8.0±0.1is reached when measured at 20-25° C. Other buffer systems can bereadily adapted to embodiments of the disclosed media compositions usingwell known protocols (see, e.g. “Buffer Solutions: The Basics” (Basics(Oxford England)) by R. J. Beynon and J. S. Easterby (1996) and “pH andBuffer Theory: A New Approach” (Wiley Series in Solution Chemistry, V.1)by H. Rilbe (1996)). In this context, the skilled artisan understandsthat a wide variety of buffer systems are well known in the art (e.g.PBS, TRIS, HEPES, MOPS, PIPES, MES, MOPSO, TAPSO, POPSO, DIPSO, HEPPSO,CAPSO, AMPSO etc.). In some embodiments of the invention, one can useTRIS with acetate, phosphate or citrate buffers at the appropriate pH.

Embodiments of the disclosed media compositions can be used to elute avariety of compounds from a variety of matrices. Illustrativeembodiments include drug elution methods that can be used for in-vitrostudies of drug eluting devices (drug blended polymer matrix). Forexample, an embodiment of the method was used with Dexamethasone sodiumphosphate (DSP) impregnated within a silicone blended matrix. Details ofthe method including the contents of the dissolution media fordetermining the DSP from the drug blended polymer matrix, with specialemphasis to drug loaded pace maker leads is disclosed herein. Suchembodiments of the dissolution media use a unique chemical mixture thatis capable of eluting the drug effectively and efficiently, providing anin-vitro platform for product development and quality control. Thedissolution media is composed of varying amounts of isopropyl alcohol(IPA), benzyl alcohol, and Diisopropyl amine (DIPA). In theseembodiments, the concentration of isopropyl alcohol was about 30% whilethe concentration of benzyl alcohol and diisopropyl amine was maintainedbelow 1% each. In a first medium embodiment, IPA in combination withDIPA was surprisingly effective for use with MCRDs made of siliconematerial. In another medium embodiment, Benzyl alcohol in combinationwith IPA was surprisingly effective for use with devices made ofpolyurethane. In addition, the combination of IPA, benzyl alcohol andDIPA was surprisingly effective for use with leads that were made ofsilicone. Such media composition embodiments therefore overcomedifficulties with elution studies relating to both the individualelution profiles of different matrix materials (e.g. silicone ascompared to polyurethane) as well as the need to be able to assess theelution profile of an agent from a matrix in a relatively short timeperiod (e.g. so as to allow a comprehensive elution study in 72 hours ofan agent that is designed to elute over at least 10, 20, 30, 60 or 90days in vivo).

The methods and compositions of the invention can be used in a varietyof contexts and are particularly well suited for studies of materialsvariations that can occur for example within a batch of processedmaterials and/or between batches of processed material. The terms“batch” and “lot” are used according to their art accepted meaning andrefers to a specific quantity of a drug or other material produced(typically according to a single manufacturing order during the samecycle of manufacture) and intended to have uniform character andquality, within specified limits. As shown in the examples below, thismedia system is proven to be discriminatory for detecting processvariations in manufacturing processes.

While the methodological embodiments of the invention can be used toassess the elution of a wide variety of compounds from a wide variety ofmatrices, these methods of the invention are particularly useful in thecontext of the manufacture of drug eluting implantable medical devices.For example, the safety and efficacy of drug coated pace maker leads arereadily evaluated using the unique dissolution methods and materialsdisclosed herein. In contrast, due to the extended release nature of theproduct and also due to the free solubility of dexamethasone sodiumphosphate, the elution of the drug is observed to be minimal inconventional media systems, for example a media that utilizes just asurfactant.

The invention disclosed herein has a number of embodiments. Oneillustrative embodiment of the invention is a method for observing theelution of a compound from a matrix, the method comprising combining thematrix comprising the compound to a solution comprising: 20-40% of alower alkanol (e.g. isopropanol); and 0.2-6.0% of a matrix swellingagent; and then assaying the solution for the presence of the compoundso as to observe the elution of the compound from the matrix into thesolution (e.g. via a chromatographic separation technique such as HPLC).In illustrative embodiments of the invention, the matrix swelling agentcomprises 0.2-1.0% diisopropyl amine; dipropylamine;tetramethylethylenediamine; or tributylamine; and/or 0.5-6% benzylalcohol. Typically, the solution further comprises a buffer such asphosphate buffer having a pH range of pH 6 to pH 8. In one illustrativeembodiment of the invention, the solution comprises 0.05M potassiumphosphate buffer at pH 8; 30% isopropyl alcohol; and <1% benzyl alcohol;or <1% diisopropylamine. Typically, the method comprises combining thematrix comprising the compound with the solution and then observing theelution of the compound from the matrix into the solution over time.

One typical embodiment of the invention is a method for observing theelution of a compound from a matrix comprising the compound into asolution. In typical embodiments of this method, the solution comprises0.03 to 0.05M potassium phosphate buffer having a pH range of pH 6 to pH8; 20-40% isopropyl alcohol; 0.5-6% benzyl alcohol; and/or 0.2-1%diisopropylamine. In one embodiment of this method, the solutioncomprises 0.03 to 0.05M potassium phosphate buffer having a pH of 6-8;30% isopropyl alcohol; and <1% benzyl alcohol; and/or <1%diisopropylamine.

Embodiments of the invention comprise a unique constellation ofcomponents that is shown to elute dexamethasone sodium phosphate moldedwith a polymer under time and conditions that allow the method to beused in the evaluation of manufacturing processes, for example toconfirm that samples from various batches have elution properties withina set of characteristic parameters. Some embodiments of the inventionmay include a 20-40% isopropyl alcohol solution having other componentsknown in the art and used in elution studies, for example phosphatebuffer having a pH range of pH 6 to pH 8 and/or anionic (e.g. sodiumdodecyl sulfate), cationic (e.g. Cetyl trimethyl ammonium bromide—CTAB)and non-ionic (e.g. Solutol HS 15-poly-oxyethylene esters of12-hydroxystearic acid, Tween 80) surfactants.

Embodiments of the method can be manipulated by modifying the conditionsunder which elution is observed, for example, by observing elution at aspecific solution temperature or temperature range, e.g. at 25, 30, 37,40, 41, 42, 43, 44 or 45 degrees centigrade or between 25 and 45 degreescentigrade. In addition, typical embodiments of the invention includethe steps of agitating the solution with a stirring device, shaker oruse a flow through device like USP apparatus 4. Typically, the volume ofthe solution used in such methods is between 50 and 150 milliliters(e.g. 50, 75, 100, or 125 milliliters). In some embodiments of theinvention, the specific formulation of the media is selected forspecific elution characteristics, for example, an ability to elute atleast 50% (or 60% or 70% or 80%) of dexamethasone sodium phosphateimpregnated within a polymeric silicone matrix in 72 hours at 37, 38,39, 40, 41, 42, 43, 44, or 45 degrees centigrade.

In describing this invention, the term “matrix” simply means anymaterial in which a compound can be coated on to, and/or combined withand/or embedded within and/or enclosed within. Similarly, the “matrixcomprising the compound” is a material having a compound such as asteroid and/or anticoagulant and/or antibiotic or the like loaded and/orcoated on it and/or embedded within it and/or enclosed within it. Suchmethods for observing the elution of a compound from a matrix byexposing the compound to a solution and then observing the presence ofthe compound in the solution over a period of time can be used toobserve a wide variety of matrices and compounds. Such assays can beused to determine what percentage of a compound (e.g. 0% up to 100% of adrug loaded compound) is eluted under specific conditions (e.g.concentration of various components of the media and/or pH and/ortemperature etc.) over various periods of time (e.g. 1 minute, 1 hour, 1day or 1 week etc.).

Elution of a compound from a wide variety of matrices are known in theart can be observed in the methodological embodiments of the invention.In typical embodiments of the invention, the matrix is an implantablepolymer matrix. Typically, polymer matrices observed in the methods ofthe invention are biocompatible and designed to minimize irritation atthe site of implantation. In certain embodiments of the invention, thepolymer may be either a biostable or a bioabsorbable polymer dependingon the desired rate of release or the desired degree of polymerstability. Biostable polymers such as polyurethanes, silicones, andpolyesters are used in certain embodiments of the invention. In theexamples provided below, the illustrative matrix used to demonstrateembodiments of the invention is a biomedical silicone polymerimpregnated with Dexamethasone sodium phosphate. Other polymers can alsobe used in certain embodiments of the invention such as polyolefins,polyisobutylene and ethylene-alphaolefin copolymers; acrylic polymersand copolymers, vinyl halide polymers and copolymers, such as polyvinylchloride; polyvinyl ethers, such as polyvinyl methyl ether;polyvinylidene halides, such as polyvinylidene fluoride andpolyvinylidene chloride; polyacrylonitrile, polyvinyl ketones; polyvinylaromatics, such as polystyrene, polyvinyl esters, such as polyvinylacetate; copolymers of vinyl monomers with each other and olefins, suchas ethylene-methyl methacrylate copolymers, acrylonitrile-styrenecopolymers, ABS resins, and ethylene-vinyl acetate copolymers;polyamides, such as Nylon 66 and polycaprolactam; alkyd resins;polycarbonates; polyoxymethylenes; polyimides; polyethers; epoxy resins,polyurethanes; rayon; rayon-triacetate; cellulose, cellulose acetate,cellulose butyrate; cellulose acetate butyrate; cellophane; cellulosenitrate; cellulose propionate; cellulose ethers; and carboxymethylcellulose. Bioabsorbable polymers include poly(L-lactic acid),polycaprolactone, poly(lactide-co-glycolide), poly(hydroxybutyrate),poly(hydroxybutyrate-co-valerate), polydioxanone, polyorthoester,polyanhydride, poly(glycolic acid), poly(D,L-lactic acid), poly(glycolicacid-co-trimethylene carbonate), polyphosphoester, polyphosphoesterurethane, poly(amino acids), cyanoacrylates, poly(trimethylenecarbonate), poly(iminocarbonate), copoly(ether-esters) (e.g. PEO/PLA),polyalkylene oxalates, polyphosphazenes and biomolecules such as fibrin,fibrinogen, cellulose, starch, collagen and hyaluronic acid. In otherembodiments of the invention, the matrix can be a metal such as one ofthe metals typically used in portions of implantable medical devicesthat are exposed to living tissue.

A wide variety of compounds can be coated on to, and/or combined withand/or embedded within and/or enclosed within a matrix to produce amatrix comprising the compound. For example, compounds examined orassayed by an embodiment of the present invention can be virtually anycompound which possesses desirable therapeutic characteristics forimplantation. In some embodiments, the compound is a glucocorticoid suchas dexamethasone, dexamethasone sodium phosphate, dexamethasone acetateor another dexamethasone derivative as well as related molecules such asbeclamethasone or betamethasone. In one illustrative embodiment of theinvention, the matrix comprising the compound is a matrix having thecompound blended therein, for example a 60-80% silicone polymer (e.g. abiomedical grade silicone polymer) impregnated with a compound such asdexamethasone sodium phosphate.

As noted above, wide range of matrix and compound materials known in theart can be studied in the methodological embodiments of the inventionincluding metal, plastic and other polymeric matrices as well ascompounds such as a steroid, an anti-coagulant an antibiotic, or ananti-inflammatory agent, for example heparin or another thrombininhibitor, hirudin, hirulog, argatroban, D-phenylalanyl-L-poly-L-arginylchloromethyl ketone, or another antithrombogenic agent, or mixturesthereof; urokinase, streptokinase, a tissue plasminogen activator, oranother thrombolytic agent, or mixtures thereof; a fibrinolytic agent; avasospasm inhibitor; a calcium channel blocker, a nitrate, nitric oxide,a nitric oxide promoter or another vasodilator; an antimicrobial agentor antibiotic; aspirin, ticlopdine, a glycoprotein IIb/IIa inhibitor oranother inhibitor of surface glycoprotein receptors, or anotherantiplatelet agent; colchicine or another antimitotic, or anothermicrotubule inhibitor, dimethylsulfoxide (DMSO), a retinoid or anotherantisecretory agent; cytochalasin or another actin inhibitor; or aremodelling inhibitor; deoxyribonucleic acid, an antisense nucleotide oranother agent for molecular genetic intervention; methotrexate oranother antimetabolite or antiproliferative agent; an anti-cancerchemotherapeutic agent; dexamethasone, dexamethasone sodium phosphate,dexamethasone acetate, belcomethasone (e.g. belcomethasone dipropionate)or another dexamethasone analog or derivative, or anotheranti-inflammatory steroid or non-steroidal antiinflammatory agent;cyclosporin or another immunosuppressive agent; trapidal (a PDGFantagonist), angiopeptin (a growth hormone antagonist), an anti-growthfactor antibody, or another growth factor antagonist; dopamine,bromocriptine mesylate, pergolide mesylate or another dopamine agonistradiotherapeutic agents; iodine-containing compounds, barium-containingcompounds, gold, tantalum, platinum, tungsten or another heavy metalfunctioning as a radiopaque agent; a peptide, a protein, an enzyme, anextracellular matrix component, a cellular component or another biologicagent; captopril, enalapril or another angiotensin converting enzyme(ACE) inhibitor; ascorbic acid, alphatocopherol, superoxide dismutase,deferoxamine, a 21-aminosteroid (lasaroid) or another free radicalscavenger, iron chelator or antioxidant of any of the foregoing; or amixture of any of these. The ratio of compound to the matrix (e.g. atherapeutic substance such as dexamethasone to a silicon polymer) willvary according to how the compound and matrix are used. A wide ratio ofcompound to matrix ratios can therefore be appropriate and can rangefrom about 10:1 to about 1:100.

As discussed above, the methodological embodiments of the invention canbe used to study matrices impregnated and/or coated with compounds thatare used or implanted in vivo including those used with pacemaker leads(e.g. in rings and tips for leads), stents, sensors, medication deliverypumps, catheters, balloons, wire guides, cannulae, and the like) and invivo and ex vivo antimicrobial coatings and similar coatings and covers.In addition, the methods and materials of the various embodiments of theinvention can be used to assay matrices and compounds that are notimplanted, such as a matrix comprising a compound that is used inindustrial application, for example, compound impregnated matrices usedin fermentation processes. Embodiments of the invention are adapted forobserving matrices produced in batches according to one or morecarefully controlled manufacturing processes (e.g. as part of amanufacturing process controlled in accordance with FDA guidelines). Anexemplary embodiment of the invention involves performing the method ona plurality of matrices produced according to a uniform manufacturingprocess. A related embodiment of the invention involves performing themethod on a plurality of such matrices made by a process designed toproduce a plurality of matrices that elute the compound at the samerate. Another embodiment of this method involves further analyticalsteps, for example comparing the elution rates of two or more ofplurality of matrices to determine if the two or more matrices have thesame or different elution rates.

A wide variety of methods known in the art can be used to observe thecompound in the solution including chromatographic methods such as HPLCand the like as well as immunoassays such as enzyme linkedimmunoadsorbent assays and the like. In view of the level of skill inthis art, artisans can use any one or a wide variety of detectiontechniques and/or any separation technique followed by detection.Illustrative but non-limiting examples of such techniques includecapillary electrophoresis, HPLC-UV; HPLC-MS (MS=Mass Spectroscopy);UPLC-UV (UPLC=Ultra performance LC) and; if for example the drug isvolatile, techniques such as gas chromatography-flame ionizationdetection (GC/FID) in GC/FID, the FID or flame ionization detectordetects analytes by measuring an electrical current generated byelectrons from burning carbon particles in the sample. See, e.g. HPLCMethod Development for Pharmaceuticals, Volume 8 (Separation Science andTechnology), 2007 Academic Press, 1^(st) ed., Ahuja and Rasmussen(Editors); and Handbook of HPLC (Chromatographic Science), 1998, MarcelDekker 1^(st) ed. Katz et al eds.

Related embodiments of the invention include compositions of matter: (1)made for; or (2) produced by the methods disclosed above, for example, acomposition of matter comprising an aqueous solution of 20-40% of alower alkanol; and one or more matrix swelling agents comprising:0.2-1.0% diisopropyl amine; 0.2-1.0% dipropylamine; 0.2-1.0%tetramethylethylenediamine; 0.2-1.0% tributylamine; or 0.5-6% benzylalcohol. In certain embodiments of this composition, the solutioncomprises 0.03 to 0.05M potassium phosphate buffer having a pH range ofpH 6 to pH 8; 30% isopropyl alcohol; <1% benzyl alcohol; and/or <1%diisopropylamine. In some embodiments of the invention, the compositionof matter further comprises a matrix impregnated with an elutable agentcomprising a steroid, an anti-coagulant an antibiotic, or ananti-inflammatory agent. Optionally for example, the matrix is a polymermatrix impregnated with dexamethasone sodium phosphate. In oneillustrative embodiment of the invention, the composition furthercomprises a polymer matrix adapted for use as part of a cardiac lead.

As noted above, certain specific embodiments of this composition ofmatter further comprise a polymer matrix impregnated with a steroid oranti-coagulant. In this context, artisans will understand that a widevariety permutations of such solutions can be readily made with minimaleffort, for example 0.03 to 0.05M potassium phosphate buffer having a pHrange of 6 to 8 (as well as half and quarter values of these numberssuch as pH 6.5 and 6.25 etc.), in combination with a swelling agent at aconcentration of 0.1%, 0.25%, 0.5%, 0.75%, 1%, 2%, 3%, 4%, 5%, or 6% (aswell as half and quarter values of these numbers such as 1.5% and 1.25%etc.), in combination with a lower alkanol at a concentration of 20%,25%, 30%, 35%, or 40% (as well as half and quarter values of thesenumbers such as 22.5% and 21.25% etc.). Certain specific embodiments ofthis composition of matter further comprise a polymer matrix impregnatedwith an agent designed to facilitate in vivo implantation of anapparatus such as a steroid or anti-coagulant.

In some embodiments of the invention, the composition of matter furthercomprises a matrix impregnated with an elutable agent comprising asteroid, an anti-coagulant an antibiotic, or an anti-inflammatory agent.Optionally for example, the matrix is a polymer matrix impregnated withdexamethasone sodium phosphate. In one illustrative embodiment of theinvention, the composition of matter further comprises a polymer matrixis adapted for use as part of a cardiac lead.

All numbers recited in the specification and associated claims (e.g. pH6 to pH 8; 0.1-6% matrix swelling agent, and 20-40% lower alkanol) areunderstood to be modified by the term “about”.

B. Apparatus for Inhibiting Evaporation from a Vessel

A variety of vessels can be used in embodiments of the elution methodsdisclosed herein, for example the well known USP apparatuses discussedbelow. In this context, one embodiment of the invention is an apparatusthat is used, for example, to facilitate the practice of the above-notedmethods by inhibiting the evaporation of an elution media from thevessels in which elution is observed. In particular, the accuracy ofquantification of a drug such as dexamethasone sodium phosphate indissolution/elution tests greatly depends upon maintaining the volume ofthe elution media. Evaporation is a significant issue due to the reducedamount of elution media used for the drug coated devices. If the volumedecreases due to evaporation, it will lead to over estimation of thedrug content. This is a significant issue in extended release productswhich are tested for a longer period of time.

Typically, the apparatus includes a cap designed to cover the vessel andinhibit elution media loss through evaporation. This evaporation losscap apparatus offers easy and accurate sampling, measuring temperatureand virtually no loss due to evaporation. Embodiments of the inventionare useful for example in the development, production and release ofdrug eluting products. For example, when a product will not be approvedby regulatory bodies without an appropriate elution method for studyingpossible process variability, the method can significantly depend uponthe integrity of the cover of the vessel. In illustrative embodiments ofthe invention provided in the examples below, the apparatus reducesevaporation to less than 1% over a period of one week. This embodimentof the invention therefore demonstrates how dramatically the inventioncan reduce the evaporation of media from a dissolution vessel.

FIG. 7 shows a typical embodiment of an apparatus of the invention, onedesigned to prevent loss due to evaporation from a fluid dissolutionvessel. This specific embodiment of the apparatus (10) comprises a cap(20) for engaging a vessel (30). The central diagram shows a group offour caps operative engaged with vessels and various interactiveelements of the apparatus. The diagram at the upper right shows the capnot engaged with a vessel and/or various interactive elements of theapparatus. In the embodiment of the invention shown in this figure, thecap has a first external side (40) and a second internal side (50) thatis exposed to a fluid contained in the vessel. The second side (50)comprises a conical member (60) that designed to direct a condensate(i.e. liquid formed by the condensation of a vapor or gas) that hascondensed from the fluid in the vessel onto the second side of the capback into the fluid. The cap includes a flange (70) disposed between thefirst external side and the second internal side of the cap. Thisembodiment shows a central port (80) disposed in the cap adapted toreceive a rotatable rod (90), where the material of the central port(typically Teflon) and the material of the rotatable rod are in closecontact so as to create a seal that inhibits escape of a materialcontained within the vessel into the external environment.

The rotatable rod in the embodiment of the invention shown in FIG. 6includes a fluid agitation member (170) at the distal end of the rodthat agitates fluid within the vessel. In this embodiment, the centralport (80) is disposed in a central washer (120) that is further disposedwithin a central washer port (130) on the cap. This embodiment shows asample port (100) disposed in the cap to allow a user to obtain a sampleof the solution from the vessel (or to introduce a composition into thevessel) via a cannula (not shown). In this embodiment, the sample port(100) is disposed in a sample port washer (110) that is further disposedin a sample washer port (160). The sample port washer (110) furtherincludes a cannula securing port (140) that receives a tightening screwmember (not shown) that can be used to secure a cannula inserted intothe sample port (100) at a desired position. This embodiment furthershows a temperature member port (150) adapted to allow a user tointroduce a temperature member that contacts and monitors thetemperature of the solution within the vessel. The temperature memberport (150) is adapted to receive a temperature port cap (210) that cancover the temperature port to prevent escape of a material within thevessel into the external environment. A sealing member (not shown) thatcontacts the vessel (30) that contains the fluid is typically disposedon the cap (20) so as to create a seal with the vessel that inhibitsescape of a material within the vessel into the external environmentwhen the cap is operatively engaged with the vessel. In addition, all ofthe interacting components in this embodiment are constructed to fittogether so as to create seals that inhibit escape of a material withinthe vessel into the external environment so that the apparatus inhibitsfluid loss from the vessel due to evaporation. This embodiment furthershows a clamp (180) that secures the cap to the vessel via a clamp screwmember (190) as well as a rack (200) constructed to hold a plurality ofvessels.

In some embodiments of the invention, the apparatus is described ashaving interacting components constructed to fit together so as tocreate seals that prevent escape of a material within the vessel intothe external environment so that the apparatus inhibits fluid loss fromthe vessel due to evaporation. In describing a device that “preventsescape of a material contained within the vessel into the externalenvironment”, this disclosure is intended for those of skill in this artwho understand that a seal that allows the escape of one molecule (or asmall number of molecules) within a vessel still prevents or essentiallyprevents the escape of a material contained within the vessel into theexternal environment. Further guidelines are provided in this regard toallow one of skill in the art to understand that prevents or essentiallyprevents escape of a material contained within the vessel into theexternal environment pertains to. These guidelines include anevaporation loss prevention cover apparatus that allows no more than10%, preferably no more than 5%, 4%, 3% or 2% and more preferably nomore than 1% of the fluid volume to escape from the vessel over a periodof 3, 4 or 5, (and optionally 7) days at 25, 37 or 45 degreescentigrade.

As noted above, a typical embodiment is an apparatus for covering avessel that contains a fluid, the apparatus comprising a cap forengaging the vessel (e.g. a circular cap), the cap having a firstexternal side and a second internal side that is exposed to a fluidcontained in the vessel, wherein the second side is cone shaped and/orcomprises a conical member that facilitates deposition of a condensatefrom the fluid back into the fluid. Typically, a flange is disposedbetween the first external side and the second internal side of the cap.In some embodiments of the invention, the flange engages an edge of thevessel so as to facilitate positioning of the apparatus in an operableorientation.

In certain embodiments of the invention, the cap includes a central portdisposed in the cap adapted to receive a rotatable rod that is used tostir a solution within the vessel. Optionally, the central port isdisposed in a central washer that is further disposed within a centralwasher port on the cap. Typically, the central port comprises a teflonmaterial (i.e. a low friction polytetrafluoroethylene polymer) disposedon a portion of the port that contacts the rotatable rod; and theportion of the central port that contacts the rotatable rod creates aseal with the rotatable rod that inhibits escape of a material containedwithin the vessel into the external environment. Some embodiments of theinvention include an apparatus kit that includes additional elements forpracticing methods of the invention such as a rotatable rod that can bedisposed in the central port, wherein the rotatable rod is disposablethrough the central port at the portion of the conical member closest tothe fluid so as to enter the portion of the vessel that contains thefluid so that the central rod acts as a fluid conduit for the condensatefrom the second side of the cap back into the fluid contained within thevessel. Typically, the rotatable rod includes a fluid agitation memberat the distal end of the rod that agitates fluid within the vessel.

In typical embodiments of the invention, the apparatus includes a sampleport disposed in the cap that is adapted to allow a user to obtain asample of the solution from within the vessel or to introduce acomposition into the vessel. Optionally, the sample port is disposed ina sample port washer that is further disposed within a sample washerport on the cap (e.g. as shown in FIG. 7). In one embodiment of theinvention, the sample port washer is disposed on the cap to guide andsupport a cannula that contacts the solution within the vessel.Typically, portions of the sample port washer that contact the cannulaand the portions of the sample port washer that contacts the samplewasher port create seals that inhibits escape of a material containedwithin the vessel into the external environment.

In certain embodiments of the invention, a portion of the apparatus thatcontacts fluid in the vessel (e.g. fluid condensate) is comprised of amaterial that is resistant to degradation by a solution comprising: 0.03to 0.05M potassium phosphate buffer at pH range of pH 6 to pH 8; 20-40%isopropyl alcohol; 0.5-6% benzyl alcohol; and 0.2-1% diisopropylamine.In other embodiments of the invention, a portion of the apparatus thatcontacts fluid in the vessel (e.g. fluid condensate) is comprised of amaterial that is resistant to degradation by a solution comprising: 0.03to 0.05M potassium phosphate buffer at pH range of pH 6 to pH 8; 1-12%limonene; 0.3-9% sodium dodecyl sulfate and 0.5-15% lower alkanol. Insome embodiments of the invention this portion is made of Delrin.Similarly, in some embodiments of the invention, the O-ring is made ofViton.

Typically, the components of the apparatus (e.g. the washers and washerports) are designed to fit together so as to create seals that preventescape of a material within the vessel into the external environment sothat the apparatus inhibits fluid loss from the vessel due toevaporation. Moreover, all portions of the apparatus that allow accessto the fluid within the vessel (e.g. the central and sample ports) canbe adapted to receive a cap member that covers the port so as to inhibitescape of a material within the vessel into the external environment. Inaddition, in typical embodiments of the invention, the cap is of unitaryconstruction, meaning that its material is made from a single cast ofmaterial and has no seams or joints that provide avenues for fluid loss.In an exemplary embodiment of the invention, the apparatus reduces fluidloss due to evaporation to less than 5%, 4%, 3%, 2% or 1% of the fluidcontained within the vessel over 7 days at 37 degrees centigrade. Inanother exemplary embodiment of the invention, the apparatus reducesfluid loss due to evaporation to less than 5%, 4%, 3%, 2% or 1% of thefluid contained within the vessel over 15 days at 37 degrees centigrade.

The methods and apparatuses disclosed herein can be adapted for use in awide variety of procedures known in the art. All patent and literaturereferences (e.g. Shah et al., International Journal of Pharmaceutics 125(1995) 99-106; AAPS PharmSci 2002; 4 (2) article 7; AAPS PharmSci 2004;6 (1) Article 11; Guidance for Industry, Extended Release Oral DosageForms: Development, Evaluation, and Application of In Vitro/In VivoCorrelations, U.S. Department of Health and Human Services Food and DrugAdministration Center for Drug Evaluation and Research (CDER), September1997, BP 2; Palamakula et al., Preparation and In Vitro Characterizationof Self-Nanoemulsified Drug Delivery Systems of Coenzyme Q10 UsingChiral Essential Oil Components, Pharmaceutical Technology OCTOBER 2004;Lawrence et al., Advanced Drug Delivery Reviews 45 (2000) 89-121 andU.S. Patent and Patent Application Nos. 6,063,314; 4,819,662; 5,464,650;5,609,629; 20040037886; and 20030208236) are incorporated by referenceherein.

Embodiments of the invention include kits comprising a first container,a label on said container, and a composition contained within saidcontainer. Such kits include elution media components in one or morecontainers having a label, the label on said container, or a packageinsert included in said container indicates that the composition can beused to elute a composition form a matrix. Optionally the kit includes apremixed, ready to use elution media. Optionally the kit includesadditional elements such as an apparatus for using the media, anembodiment of which is shown in FIG. 7. Other embodiments of theinvention include a kit containing an apparatus for using the media, anembodiment of which is shown in FIG. 7, in the absence of elution mediacomponents.

EXAMPLES Example 1 Illustrative Methods and Materials Used to PracticeEmbodiments of the Invention Elution Procedure Typical DissolutionSystem Setup

The following provides illustrative methods and materials useful withembodiments of the invention. It is to be understood, however, thatthese illustrative examples, while indicating some embodiments of thepresent invention are given by way of illustration and not limitation.Many changes and modifications within the scope of the present inventionmay be made without departing from the spirit thereof, and the inventionincludes all such modifications.

Illustrative elution parameters are shown in Table 1.

TABLE 1 Typical Elution Parameters Parameter Specification IllustrativeApparatus USP Apparatus 2 with mini vessels, mini paddles, covered bylow evaporation loss covers and/or USP Apparatus 1 with mini vessels,mini baskets, covered by low evaporation loss covers Other USPdissolution apparatus or modifications therein can be used. IllustrativeMedia 0.05M phosphate buffer having at pH 8; Information 30%isopropanol; and <1% diisopropyl amine, or <1% benzyl alcoholIllustrative Media 75 ml Volume Illustrative Media 45.0 ± 0.5° C.Temperature: Illustrative Media 1 ml withdrawn/replaced IllustrativeShaft Speed 100 rpm Illustrative Evaporation Special low evaporationloss covers Control Typical Time Points* 6 hr, 12 hr, Day 1, Day 2, Day3, Day 4, Day 6, Day 8, Day 10, Day 12

Method Development

The steps in method development can include adaptations of methods andmaterials known in the art, for example USP General Chapter <1092>,In-Process Revision, “The Dissolution Procedure: Development andValidation”, Pharmacopeial Forum, 2005, 31 (5), p. 1463; Burgess et al.,“Assuring Quality and Performance of Sustained and Controlled ReleaseParenterals: Workshop Report”, AAPS PharmSci, 2002, 4(2), article 7; andBurgess et al., “Assuring Quality and Performance of Sustained andControlled Release Parenterals: EUFEPS Workshop Report”, AAPS PharmSci,2004, 6(1), article 11.

A first step can be to determine the solubility of the product usingstandard aqueous elution media, several of which are listed in the USP(see, e.g. USP General Chapter <724>, “Drug Release”), literature (see,e.g. Noory et. al., (Food and Drug Administration—CDER), “Steps forDevelopment of a Dissolution Test for Sparingly Water-soluble DrugProducts”, Dissolution Technologies, 2000, 7(1), Article 3) and the USFDA website (see, e.g. FDA website link for elution/dissolution mediasusing search terms: “accessdata.fda.gov/scripts/cder/dissolution/”). Theinitial run can allow evaluation of the effect of pH on the product. Ifthe product exhibits poor dissolution, then the need for further agentssuch as surfactants (below the critical micelle concentration formingemulsions) can be evaluated.

Dexamethasone sodium phosphate is a steroid, freely soluble in water.Dexamethasone sodium phosphate is typically distributed in the polymermatrix of a implantable medical device such as a cardiac lead as adispersion. The drug generally diffuses from the matrix into the fluidicsystem where the lead is placed. In typical embodiments of theinvention, it is important to use a dissolution medium that exhibitsgood thermodynamic compatibility with the polymer (see, e.g. Peppas etal., “Modeling of Drug Diffusion through Swellable Polymeric Systems”,Journal of Membrane Science, 1980, 7, p. 241-253; and Paul, D. R.,“Controlled Release Polymeric Formulations”, ACS Symposium Series,volume 33, ACS, Washington, 1976.

A literature survey showed that the elution of dexamethasoneacetate-eluting cardiac pacing electrodes is less than 19% in 24 days ifPBS (without additives) is used (see, e.g. Casas-Bejar et. al., “MedicalElectrical Leads and in-dwelling Catheters with enhancedBiocompatibility and Biostability”, United States Patent Publication,Publication # US 20020138123 A1, Application Number 998536, Sep. 26,2002) (PBS=Phosphate Buffered Saline). Another study conducted byGuidant Corporation, showed elution at about 10% in 30 days (see, e.g.Heil, R (Guidant Corporation), “In Vivo Comparison ofDexamethasone-eluting cardiac pacing electrode technologies withdifferent release rates”, Proceed. Int'l. Symp. Control. Rel. Bioact.Mater., 2000, 27, p. 471). The percent elution was less than 7% in 10days from the CRD leads when PBS (pH 5) without any additives was used.The information indicates that though the drug may be soluble in thebuffered media at low concentrations (see sink condition evaluationbelow), the drug dissolution will be controlled by diffusion from thepolymer.

Preparation of Device for Elution Studies

The drug eluting portion of samples can be cut separately from thedevice and used for the purpose of testing. The CRD section can be cutfrom the device such that the length of the section can be approximately1-2 cm.

Choice of Elution Parameters

To evaluate buffers with different pH, Dexamethasone sodium phosphatecan be dissolved in an elution media (e.g. one of the differentembodiments of the invention disclosed herein). The stability ofDexamethasone sodium phosphate with respect to pH follows this order: pH4>pH 7.5>pH 9. This concentration was about 10 times the concentrationthat might be observed if the drug from the typical device wascompletely eluted in about 75 mL of media.

A next step can involve attempting to increase the elution by addingdifferent types of additives, capable of forming macro-emulsions, to themedia. This can be in concurrence with the USP, US FDA and industryguidelines for performing elution on a sparingly soluble drug substance(see, e.g. USP General Chapter <1092>, “The Dissolution Procedure:Development and Validation”, Pharmacopeial Forum, 2005, 31 (5), p. 1463;FDA Guidance for Industry (CDER), “Extended Release Oral Dosage Forms:Development, Evaluation and Application of In Vitro/In VivoCorrelations”, September 1997; FDA Guidance for Industry (CDER),“Immediate Release Solid Oral Dosage Forms Scale-Up and PostapprovalChanges: Chemistry, Manufacturing, and Controls, In Vitro DissolutionTesting, and In Vivo Bioequivalence Documentation”, November 1995; 4.Burgess et al. “Assuring Quality and Performance of Sustained andControlled Release Parenterals: Workshop Report”, AAPS PharmSci, 2002,4(2), article 7; Burgess et al., “Assuring Quality and Performance ofSustained and Controlled Release Parenterals: EUFEPS Workshop Report”,AAPS PharmSci, 2004, 6(1), article 11, respectively). The suitability ofdifferent classes of surfactants, namely, anionic (e.g. sodium dodecylsulfate), cationic (e.g. Cetyl trimethyl ammonium bromide—CTAB) andnon-ionic (e.g. Solutol HS 15-poly-oxyethylene esters of12-hydroxystearic acid, Tween 80) as an additive to the elution mediacan be evaluated.

Choice of Apparatus

The apparatus chosen for this method can be that shown for example inFIG. 7 or one known in the art such as USP Apparatus 2 (Paddles). Due tothe low content of the drug in the device, mini vessels with minipaddles can be chosen for the method. The apparatus can be set at 100rpm. A media volume of 75 mL is appropriate for the analytical methodsdetection capability and meets typical the sink conditions. The mediacan be maintained at 32-45° C.±0.5° C. The sample pull volume can be 1mL at each time point with media compensation, in line with elutionguidelines.

Choice of Analytical Method of Quantification of Dexamethasone SodiumPhosphate

The initial choice of analytical method can be UV-Vis. However, due tothe low concentration of drug present in the material, HPLC with UVdetection can also be used

The mobile phase preparation and choice of the column can be instructedin the agent (e.g. Dexamethasone sodium phosphate) monograph. Thechromatographic column (USP L11) used can be an Phenomenex LunaHexyl-Phenyl 4.6 mm×250 mm, 5 μm. A gradient can be used with 1 mL/minflow rate. The run time can be about 35 minutes. The UV detectionwavelength can be 254 nm, where the method can be found to be specificfor quantification of Dexamethasone Sodium phosphate in the elutionmedium. The injection volume for standard and samples can be 100 μL.

Sampling Time Points and Elution Data

The elution of Dexamethasone sodium phosphate from a CRD can be examinedusing embodiments of the invention disclosed herein. FIGS. 1-6 showtypical plots of elution of dexamethasone sodium phosphate from CRDs.The elution pattern for CRD were similar to the profile of anon-disintegrating product (see, e.g. Hanson, R., Gray, V., Handbook ofDissolution Testing, Page. 22, 3^(rd) Edition, Dissolution Technologies,Inc, Hockessin, Del.). This profile was generally obtained where thedissolution rate was determined by the process of diffusion anddissolution.

As shown in FIGS. 1-6, different nominal lots of the typical CRD can beanalyzed using the embodiments of the invention.

Elution Discrimination Studies

As shown in FIGS. 1-6, the discriminating nature of the elution methodcan be used to study differing lots of the same device. One lot canmanufactured using the nominal process and other lots can bemanufactured with different process variations. The elution method canbe used to discriminate between the nominal and process variation lots.

All patent and literature references cited in the present specificationare hereby incorporated by reference in their entirety.

1. A method for observing the elution of a compound from a matrix intoan aqueous media, the method comprising exposing a matrix comprising thecompound to a media, wherein the media comprises: 20-40% of a loweralkanol; 0.2-6.0% of a matrix swelling agent; and assaying the media forthe presence of the compound so as to observe the elution of thecompound from the matrix into the media.
 2. The method of claim 1,wherein the media comprises: 0.03 to 0.05M phosphate buffer having a pHrange of pH 6 to pH
 8. 3. The method of claim 1, wherein the matrixswelling agent comprises at least: 0.2-1.0% diisopropyl amine; 0.2-1.0%dipropylamine; 0.2-1.0% tetramethylethylenediamine; 0.2-1.0%tributylamine; or 0.5-6% benzyl alcohol.
 4. The method of claim 3,wherein the media comprises: 0.05M phosphate buffer having at pH 8; 30%isopropanol; and <1% diisopropyl amine, or <1% benzyl alcohol.
 5. Themethod of claim 1, further comprising performing the method on aplurality of matrices made by a process designed to produce a pluralityof matrices that elute the compound at the same rate and comparing theelution rates of two or more of plurality of matrices to determine ifthe two or more matrices have the same or different elution rates. 6.The method of claim 1, wherein the media is assayed for the presence ofthe compound using high performance liquid chromatography (HPLC).
 7. Themethod of claim 6, wherein the matrix comprising the compound is apolymer matrix having the compound blended therein.
 8. The method ofclaim 7, wherein the matrix comprises a biomedical grade siliconepolymer or a biomedical grade polyurethane polymer.
 9. The method ofclaim 1, wherein the compound comprises a steroid, an anti-coagulant anantibiotic, or an anti-inflammatory agent.
 10. The method of claim 9,wherein the compound is dexamethasone sodium phosphate.
 11. The methodof claim 1, wherein the matrix comprising the compound is implantable invivo.
 12. The method of claim 1, further comprising observing elution ata media temperature of between 25 and 45 degrees centigrade.
 13. Themethod of claim 1 further comprising agitating the media with a stirringdevice.
 14. The method of claim 1, wherein the volume of the media isbetween 50 and 150 milliliters.
 15. The method of claim 1, furthercomprising using a media in the method that is selected for its abilityto elute at least 50% of dexamethasone sodium phosphate impregnatedwithin a polymeric silicone in 72 hours at 45 degrees centigrade.
 16. Acomposition of matter comprising an aqueous solution of: 20-40% of alower alkanol; and one or more matrix swelling agents comprising:0.2-1.0% diisopropyl amine; 0.2-1.0% dipropylamine; 0.2-1.0%tetramethylethylenediamine; 0.2-1.0% tributylamine; or 0.5-6% benzylalcohol.
 17. The composition of matter of claim 16, wherein the loweralkanol is isopropanol.
 18. The composition of matter of claim 16,wherein the media comprises: 0.03 to 0.05M potassium phosphate bufferhaving a pH range of pH 6 to pH 8; 30% isopropanol; and <1% diisopropylamine, or <1% benzyl alcohol.
 19. The composition of matter of claim 16,further comprising a matrix impregnated with an elutable agentcomprising a steroid, an anti-coagulant an antibiotic, or ananti-inflammatory agent.
 20. The composition of matter of claim 19,wherein the matrix is adapted for use as part of a drug eluting medicaldevice.